This invention relates to an apparatus for positioning a sample. There has been a demand for an apparatus having a high accuracy in positioning the sample and having a short time for positioning or manufacturing the sample. For attaining this object, conventional apparatuses for positioning a sample have utilized a stage with a coarse adjustment driving structure and with a fine adjustment driving structure for stepwise moving the sample a fine adjustment for positioning the sample utilizes the fine adjustment driving structure after a coarse adjustment utilizing a coarse adjustment driving structure for positioning the sample.
For instance, an apparatus for positioning a sample is disclosed in Japanese Laid-Open Patent No. 53-64478; one of the inventors is the same as that of the present invention; Japanese Laid-Open Patent No. 53-64478 is entitled "Apparatus for positioning sample" and was published on Jun. 8, 1978. This reference discloses that a fine adjustment stage and the driving structure are able to move along three dimensions corresponding to X, Y and Z axes on a coarse adjustment stage which is also movable along the dimensions of the X, Y and Z axes.
Japanese Laid-Open Patent No. 2-13915 entitled "Sample move apparatus, sample move system and semiconductor manufacture apparatus" was published on May 29, 1990 and discloses in FIG. 1 thereof that a fine adjustment stage, which is able to move along the three dimensions corresponding to the X, Y and Z axes, finely rotates in a plane containing the X and Y axes and moves along a fine slope towards the upper and lower directions, is formed with one through hole along the upper and lower directions at the stage, and a coarse adjustment stage, which is movable along the X, Y and Z axes within the through hole and is independent from the fine adjustment stage.
The apparatus of Japanese Laid-Open Patent No. 2-13915 changes the upper and lower positional relationship between the fine adjustment stage and the coarse adjustment stage through the Z axis driving structure and passes a sample hold base mounted on either the fine adjustment stage or the coarse adjustment stage from the fine adjustment stage to the coarse adjustment stage and vice versa. As the sample is positioned by the coarse adjustment stage, the upper surface of the coarse adjustment stage is elevated higher than the upper surface of the fine adjustment stage, and the coarse adjustment stage adsorbs and holds the sample hold base through chucks. As the sample is positioned by the fine adjustment stage, the upper surface of the fine adjustment stage is elevated higher than the coarse adjustment stage, and the fine adjustment stage holds the sample hold base for positioning the sample and positions the sample to each direction.
The apparatus of Japanese Laid-Open Patent No. 2-13915 does not mount the fine adjustment stage on the coarse adjustment stage. Although the apparatus of Japanese Laid-Open Patent No. 53-64478 mounts the fine adjustment stage on the coarse adjustment stage. The apparatus of Japanese Laid-Open Patent No. 2-13915 independently moves the coarse adjustment stage from the fine adjustment stage. Accordingly, the apparatus of Japanese Laid-Open Patent No. 2-13915 moves the coarse adjustment stage with a light load, and the starting current and driving current of the driving structure is small. Thus, the power consumption and generated heat amount of the apparatus is small. Correspondingly an air draft caused by the generated heat of the apparatus is small so that an error in the length measurement by using a laser is small. However, the prior arts require the following improvements.
Recently, there has been a tendency to make the sample, for instance a wafer, to a larger size such as 8inches; correspondingly the sample hold base must also be made to large size, and an exposure area of the sample is expanded so that the range of movement of the sample hold base is also expanded.
In such a larger apparatus, when the wafer is positioned by using the apparatus illustrated by Japanese Laid-Open Patent No. 2-13915, the coarse adjustment stage moves the sample hold base first stepwise, then the sample hold base is passed from the coarse adjustment stage to the fine adjustment stage for a fine positioning of the sample hold base. At this time, the coarse adjustment stage is returned to the initial position in which the coarse adjustment stage is not moved. Repeating the above mentioned operation by using the coarse adjustment stage and the fine adjustment stage, the exposure to the sample and the electron beam lithography to the sample take place.
When the coarse adjustment stage is moved stepwise, the positional relationship between the coarse adjustment stage and the fine adjustment stage is varied. Accordingly, the coarse adjustment stage does not always hold or chuck the center of the sample hold base or the periphery of the center, and sometimes the coarse adjustment stage holds or chucks merely one end portion of the sample hold base.
When the sample hold base is a larger scale, and the coarse adjustment stage holding the sample hold base chucks the portion of one end of the sample hold base, the coarse adjustment stage or its supporting structure is deflected as a result of the weight itself so that the sample hold base or the sample mounted on the sample hold base is badly influenced by the deflection.
The large-scaled wafer or sample hold base causes the large-scaled chuck structure of the coarse adjustment stage to suffer additional problems. When a large-scaled electromagnetic chuck is used for holding the sample hold base, the generated quantity of heat caused by the driving current of the apparatus increases. When the generated heat is transferred to the sample hold base in expanding the sample hold base thermally, the positioning of the sample hold base is adversely effected. The air fluctuation above the light passage from the laser length measurement equipment, which is generated by the heat of the equipment, prevents the equipment from obtaining an accurate measurement of the length.
When the coarse adjustment stage is supported at one point, which is not the center of the stage, and is advanced directly in the directions of the X and Y axes, a rotational force is applied to the coarse adjustment stage for rotating the stage around one supporting point of the sample hold base.